Re: [PATCH] mmc: core: Do not hold re-tuning during CMD6 commands

[Adrian Hunter]

On 24/03/17 10:32, Chaotian Jing wrote:
> On Fri, 2017-03-24 at 09:52 +0200, Adrian Hunter wrote:
>> On 24/03/17 08:19, Chaotian Jing wrote:
>>> this patch is refine for 'commit c6dbab9cb58f ("mmc: core: Hold re-tuning
>>> during switch commands")'
>>> Since it has 3 retries at max for CMD6, if the first CMD6 got CRC error,
>>> then should do re-tune before the next CMD6 was sent.
>>>
>>> Signed-off-by: Chaotian Jing <chaotian.jing@xxxxxxxxxxxx>
>>> ---
>>>  drivers/mmc/core/mmc_ops.c |    3 +--
>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
>>> index fe80f26..6931927 100644
>>> --- a/drivers/mmc/core/mmc_ops.c
>>> +++ b/drivers/mmc/core/mmc_ops.c
>>> @@ -534,8 +534,6 @@ int __mmc_switch(struct mmc_card *card, u8 set, u8 index, u8 value,
>>>  	bool use_r1b_resp = use_busy_signal;
>>>  	unsigned char old_timing = host->ios.timing;
>>>  
>>> -	mmc_retune_hold(host);
>>> -
>>>  	/*
>>>  	 * If the cmd timeout and the max_busy_timeout of the host are both
>>>  	 * specified, let's validate them. A failure means we need to prevent
>>> @@ -567,6 +565,7 @@ int __mmc_switch(struct mmc_card *card, u8 set, u8 index, u8 value,
>>>  		cmd.sanitize_busy = true;
>>>  
>>>  	err = mmc_wait_for_cmd(host, &cmd, MMC_CMD_RETRIES);
>>> +	mmc_retune_hold(host);
>>
>> That is not how mmc_retune_hold() works, you need mmc_retune_hold_now() as
>> it is here:
>>
>> 	https://marc.info/?l=linux-mmc&m=148940903816582
>>
>> But using "retries" with commands that have busy-waiting on the data line
>> doesn't make much sense anyway.  Particularly with CRC errors, I would
>> expect the card is actually busily doing the switch and we need only to wait
>> for it.  The same can be true for timeout errors.  For some CMD6 we might
>> need to send CMD12 if the card is busy after an error.  I would prefer an
>> explicit attempt at recovery from CMD6 errors.
>>
> 
> It's the host driver's responsibility to ensure card is not in busy
> state before issue the next R1B command, or the MMC core layer needs do
> extra check/waiting before issue a R1B command.

Better to deal with cards stuck in busy from the places where busy-waiting
is expected.

> I think the purpose of "re-tune" is trying to cover particular case(eg.
> voltage fluctuate or EMI or some glitch of host/device which caused CRC
> error)

No, re-tuning is to compensate for drift caused primarily by temperature change.

> error) , but in such cases, too many cases are disable re-tune function
> by mmc_retune_hold(), for example, in this case, if a response CRC error
> got then we never have chance to recover it. then cause system cannot
> access emmc or suspend/resume fail.

Maybe you have a hardware problem.